Conventionally, in printers, a plurality of unit substrates are provided such as a memory substrate, etc., other than a main substrate (control substrate), and such unit substrates are connected by cables or slots, etc.
In a system with a function of printing image data obtained from a personal computer (PC) by a printer, the PC and the printer are connected by a cable.
Namely, a printer is used by connecting a plurality of units (unit substrates, PC) to a device main body (printer main body, main substrate).
Japanese Unexamined Utility Model Publication 8-001388/1996 (published on Sep. 13, 1996), and Japanese Unexamined patent publication 62-267674/1987 (published on Nov. 20, 1987) disclose the technique (connection checking system) for detecting if the foregoing unit is appropriately mounted to the device.
According to the connection checking system of Japanese Unexamined Utility Model Publication 8-001388/1996, a detection terminal is mounted to the connector installation section of the substrate, and a short-circuit elastic contact terminal is provided outside the cabinet of the connector of a cable for connecting the unit, and the mounted state of the connector is checked by detecting if the detection terminal and the short-circuit elastic contact terminal are conducted.
Japanese Unexamined patent publication 62-267674/1987 discloses the connection checking system for determining the state (ON or OFF) (connected state of each sensor) of a device provided with a plurality of sensors (units).
In the foregoing conventional structure, a determination voltage is applied to a circuit (ladder circuit) wherein a plurality of paired series of resistance and sensor are connected in parallel and current flows in a resistance which makes a pair with the sensor in the ON state. Further, by setting the respective values of the resistances (partial pressure ratio) to be appropriate values and measuring a total amount of voltage dropped in the overall circuit, the state (ON or OFF) of each sensor can be detected.
In the connection checking system of Japanese Unexamined Utility Model Publication 8-001388/1996, a detection terminal and an elastic contact terminal dedicated for checking the connected state are needed, and a problem therefore arises in that the manufacturing cost of the device increases.
Also in the connection checking system of Japanese Unexamined patent publication 62-267674/1987, special wiring and terminal are needed for the application of the determination voltage, and the foregoing problem of an increase in the manufacturing cost of the device cannot be avoided.